A cardiac myosin ATPase inhibitor (IC50 = 0.3 μM); selective for cardiac myosin over skeletal myosin (IC50 = 4.7 μM); slows ATPase activity of α- and β-myosin; reduces cardiac contractility, prevents left ventricular hypertrophy, and reverses pathologic remodeling in mouse models; relieves left ventricular outflow tract obstruction in cats